1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking a plurality of fuel cells together. Each of the fuel cells is formed by stacking a membrane electrode assembly and separators together. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, the electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly make up a power generation cell (unit cell) for generating electricity. In use, typically, several tens to several hundreds of the power generation cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.
In the fuel cell, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, for every power generation cell or for every a predetermined number of power generation cells, one coolant flow field is formed between the adjacent separators, for supplying a coolant within electrode areas along surfaces of the separators.
Further, mostly, the fuel cell of this type adopts so called internal manifold structure. Specifically, a fuel gas supply passage and a fuel gas discharge passage, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage, and a coolant supply passage and a coolant discharge passage are formed in the fuel cell for allowing the fuel gas, the oxygen-containing gas, and the coolant to flow through the power generation cells in the stacking direction.
For example, a fuel cell stack disclosed in International Publication No. WO 2010/082589 includes power generation units each formed by stacking an electrolyte electrode assembly and metal separators. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. Each of the metal separators has rectangular surfaces. The metal separator has a wavy gas flow field on its surface facing the electrode for supplying the fuel gas or the oxygen-containing gas as a reactant gas along the electrode. The power generation units are stacked together such that a coolant flow field, which corresponds to the back surface shape of the wavy gas flow field, is formed between the adjacent power generation units.
Further, a reactant gas supply passage and a reactant gas discharge passage as passages of the reactant gas extend respectively through two opposite sides of the metal separators in the stacking direction for allowing the reactant gas to flow through the reactant gas supply passage and the reactant gas discharge passage. A pair of coolant supply passages and a pair of coolant discharge passages as passages of the coolant extend through the other two opposite sides of the metal separators in the stacking direction, at least adjacent to the reactant gas supply passage or the reactant gas discharge passage, for allowing the coolant to flow through the coolant supply passages and the coolant discharge passages. The pair of coolant supply passages are arranged on the respective sides, while the pair of coolant discharge passages are also arranged on the respective sides.
Since the pair of coolant supply passages are provided separately on the two opposite sides and the pair of coolant discharge passages are also provided separately on the two opposite sides, it is possible to supply the coolant uniformly and reliably to the entire coolant flow field.